Use stackalloc for multiple instances of arrays of constant size

[Mrnikbobjeff]

Description

Referencing #11846
searching for 'new char[' / 'new int[' reveals several instances where we allocate tiny temporary char arrays on the heap instead of stackallocing them.
This search reveals multiple simple optimizable instances.

Public API Changes

None

Intended Use-Case

Removing unnecessary allocations

[MartyIX]

Why don't you simply create a PR for it?